A nonce is an arbitrary number intended for one-time use. It is often combined with a fine-grained timestamp to ensure that its identity is associated with a single point in time. A nonce does not need to be a random number, but generating a pseudorandom nonce is one way to increase its effectiveness.
A cryptographic nonce is used in cryptography to enhance secure communications. For instance, a nonce may be part of a two-factor authentication system, where one of the factors may be used only once.